How to create a 3-in-1 bootable USB drive on Linux

A USB drive with only 1 partition* to load GRUB2 on USB-bootable machines with Legacy BIOS, 64-bit UEFI or 32-bit UEFI.

*Due to the maximum size of a file inside an EFI system partition, files of 4 GiB or larger (such as some ISO images) must be placed on another partition. That second partition can be of type ext4, for instance.

Partition the drive and install GRUB2

Warning : the USB drive will be formatted, save your data before proceeding!

First of all, on your current installation, check if the folder /usr/lib/grub/ exists and is not empty. If it is empty or does not exist, make sure the package grub-common (or equivalent for your distribution) version 2 or higher is installed. Depending on the system, /usr/lib/grub/ will contain one or more of the following folders : x86_64-efi, x86_64-efi-signed, i386-pc, i386-efi, ...

The x86_64-efi, i386-pc and i386-efi folders need to be present in order to install the corresponding bootloader on the USB drive.

Install them using the package manager, for instance on Ubuntu :

sudo apt install --no-install-recommends --yes grub-pc-bin grub-efi-ia32-bin grub-efi-amd64-bin

Now, find the device file for your USB drive. Here, the file is /dev/sdX. Replace X with the appropriate lower case letter(s) in the commands.

Make sure it's the right drive (check the capacity and the partitions) :

sudo fdisk -l /dev/sdX

Open fdisk :

sudo fdisk /dev/sdX

Press the following keys (THIS WILL ERASE ALL DATA FROM THE SELECTED DRIVE) :

o <enter> # Create a new empty DOS partition table

n <enter> # Create a new partition

p <enter> # Select primary partition type

1 <enter> # Set partition number to 1

<enter> # Start partition at the first possible sector (default)

<enter> # Set partition end to the last possible sector (default)

Note : if you are asked whether the partition signature should be deleted, then answer yes.

t <enter> # Change partition type

e f <enter> # Set partition type to EFI (FAT-12/16/32)

a <enter> # Enable the bootable flag on partition 1

w <enter> # Write the partition table

Create a fresh filesystem in the newly created partition :

sudo mkfs.fat -F32 /dev/sdX1

Mount the filesystem :

sudo mount -o umask=000 /dev/sdX1 /mnt

Write the MBR and install the GRUB files required for legacy BIOS boot on the drive :

sudo grub-install --no-floppy --boot-directory=/mnt/boot --target=i386-pc /dev/sdX

Install /EFI/BOOT/BOOTX64.EFI and other GRUB files required to load GRUB from a 64-bit UEFI firmware :

sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt --target=x86_64-efi /dev/sdX

Install /EFI/BOOT/BOOTIA32.EFI and other GRUB files required for a 32-bit UEFI :

sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt --target=i386-efi /dev/sdX

Create a grub.cfg file :

touch /mnt/boot/grub/grub.cfg

Example grub.cfg with Xubuntu 22.04 Live

Notes :

• Skip this part if you already have a working grub.cfg for the USB drive.
• Other examples can be found in this repository's grub.cfg file.

Create a folder for ISO images :

mkdir /mnt/isos

Download a Xubuntu ISO image (for example : Xubuntu 22.04 64-bit) :

Note : make sure there is enough space on the USB drive.

wget --directory-prefix=/mnt/isos http://cdimages.ubuntu.com/xubuntu/releases/jammy/release/xubuntu-22.04.5-desktop-amd64.iso

Edit grub.cfg :

nano /mnt/boot/grub/grub.cfg

Paste (and ajust) this simple GRUB config file :

if [ "${grub_platform}" = "efi" ]; then rmmod tpm; fi # See https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1851311
menuentry 'Xubuntu 22.04 amd64' {
	set isofile="/isos/xubuntu-22.04.5-desktop-amd64.iso"
	#search --set=root --file $isofile # Uncomment if the bootloader and OS files are on different partitions
	loopback isoloop $isofile
	linux (isoloop)/casper/vmlinuz locale=en_US console-setup/layoutcode=us boot=casper iso-scan/filename=$isofile quiet --
	initrd (isoloop)/casper/initrd
}

Notes about kernel boot parameters :

• Boot parameters used in the above example are specific to Ubuntu and its variants.
• locale= sets the language of the live system. Valid values include en_US, pt_BR, zh_CN, fr_FR, ...
• console-setup/layoutcode= sets the keyboard layout. Some possible values are us, br, cn, fr, ...

Press the following keys :

CTRL+O <enter> # Save grub.cfg

CTRL+X # Exit nano

Finish

Unmount the filesystem :

sudo umount /mnt